JPH05126613A - Measuring element - Google Patents

Abstract

PURPOSE: To provide a measurement element which is strong against expansion of finger of a measurement element. CONSTITUTION: A surface area 38 of a substrate 11 is not coated between, in flow direction 37, a front flow side edge 12 and a resistor path 20 against a measurement resistor 23, and a substrate area supporting the resistor path 20 against the measurement resistor 23 is extended in the flow direction 37, and separated from different each resistor path 20 by a slit 39 originating from a flow-out edge 13 of the substrate 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring element for a mass flow rate measuring device of a fluid medium, for example, intake air of an internal combustion engine, which supports a plurality of resistance paths exposed to the fluid medium. A substrate, and the resistance paths are distributed and arranged on the substrate as follows, that is, the resistance paths for the measurement resistance are distributed and arranged in the flow direction in the vicinity of the outflow side edge behind the board. The measuring element being used.

[0002]

In a device known as a hot film air flow meter, the resistance path of the temperature sensor and the compensation resistance, on the one hand, and the resistance path of the measurement resistance, on the other hand, together with the two balancing resistances form a Wheatstone bridge. The bridge diagonal voltage of this bridge is applied to the control amplifier. The output voltage of the control amplifier is used as the heating voltage for the heating resistance of the measuring element. The resistance path for the measuring resistance and the heating resistance of the measuring element is then arranged on the substrate so that there is good thermal contact between them. Thereby,
The measured resistance is brought to high temperatures well above the media temperature. Now, when the flow rate flowing through the measuring element changes, the temperature of the measuring resistance changes due to the change in convective heat transfer. And since the measured resistance has a temperature coefficient different from zero, the Wheatstone bridge detunes. Based on this, the control amplifier changes the output current to the heating resistor. Through the closed control loop, changes in the measured resistance due to the amount of heat entering and exiting are compensated by changes in the heating capacity of the heating resistance. Therefore, the heating current or output voltage of the control amplifier is a measure for the flow rate of the flowing medium. Fluctuations in the temperature of the flowing medium are corrected by a series circuit of a temperature sensor and a compensation resistor.

In a known measuring element of the type mentioned at the outset for the device (DE 3638138 A1), the distribution of the resistance paths on the substrate is such that the resistance paths are arranged in tandem parallel to one another in the flow direction. The resistance path for the compensating resistance is then arranged on the same side of the substrate between the resistance path for the temperature sensor and the resistance path for the measuring resistance, and the resistance path for the heating resistance is on the other side of the substrate It is arranged so as to directly face the resistance path for. The individual resistance paths are separated from each other in the substrate by slits extending perpendicular to the flow direction. This results in good temperature decoupling between the resistance paths. Due to this separating slit, the substrate has three fingers of the same length. The first two of these fingers in the flow direction each carry one resistance path, and the last finger in the flow direction supports the resistance path for the measuring resistance and the heating resistance. However, it has been found that even with careful manufacturing and optimal bonding, the finger spread cannot be completely eliminated, and the fingers are displaced from the optimum flow relatively frequently, especially with different magnitudes of displacement. When the flowing medium flows around the measuring element,
The widening of this finger has a great influence on the shape of the boundary layer, which leads to an increase in defects with respect to the required characteristic curve of the measuring element.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a measuring element having a simple structure which is not affected by the spread of fingers.

[0005]

According to the invention, the surface area of the substrate is not covered between the front inflow side edge in the flow direction and the resistance path for the measuring resistance, and the resistance for the measuring resistance is The substrate region supporting the path is arranged and solved in such a way that it is separated from each other resistance path by a slit extending from the outflow edge of the substrate in the flow direction.

The measuring element according to the invention having the features of claim 1 or 4 avoids the disadvantages associated with the spreading of the fingers.

In the structure of claim 1, the slit extending perpendicularly to the flow direction is omitted, and the temperature decoupling of the resistance path of the measurement resistance and the other resistance path, which is necessary for a small layout, is achieved in the flow direction. With a slit parallel to.
Such a construction and the provision of an uncovered flat inflow side in front of the resistance path of the measuring resistance makes the measuring element robust against finger spreading. The resistance paths of the measuring resistance and the required heating resistance are preferably arranged opposite one another on different sides of the substrate. The resistance path of the measuring resistance is then arranged on the same side of the substrate as the other resistance paths.

According to another aspect of the present invention, the flow medium directly flows into the individual resistance paths by the stepwise step of the measuring element. This makes the measuring element robust against the spread of the fingers even in the following cases. That is, according to another embodiment of the present invention, for another temperature decoupling, the slits are provided in the substrate perpendicular to the flow direction, and the slits are arranged in line with the inflow side edges of the individual resistance paths. Even in case of.

In the measuring element according to the invention, a costly inspection process for the finger flare is omitted. This makes the manufacturing process cheaper. The outer contour of the substrate is cut from the large substrate using a laser. This contour is a simple rectangle in the first embodiment of the invention, and in the second embodiment it is a stepped contour which extends along the longitudinal edge indicating the flow direction.

In the two variants of the invention as well, the inflow edge of the substrate or the inflow edge of the individual steps can be designed to be flow-friendly in order to adapt to the ambient flow of the measuring element.

By means of another embodiment, advantageous modifications and improvements of the measuring element according to claims 1 to 4 are achieved.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An exemplary hot film air mass meter for a typical fluidized medium mass flow measuring device shown in FIG. The measuring element 10 is exposed to a fluid medium, here air, and in the case of a motor vehicle is arranged in a bypass to an air intake sleeve. The direction of flow of the flowing air is indicated by arrow 37. Measuring element 10
Consists of a substrate and a number of resistive paths 20. The substrate is cut out from a large substrate by using a laser. The resistance path 20 is arranged on the surface of the substrate 11. The substrate 11 has a rectangular shape, and one of the longer sides in the flow direction is cut out in a stepwise manner. As a result, three steps 14, 15, 1 from the inflow side edge 12 on the front side in the flow direction as viewed in the flow direction to the outflow side edge 13 on the rear side in the flow direction of the substrate 11.
6 has occurred. In that case, the subsequent stages 15, 16 respectively
Respectively project beyond the preceding steps 14,15. The first stage 14 is defined by the leading inflow edge, and the two next stages 15, 16 are the inflow edge 1
It has 7 to 18. A resistance path 20 is arranged in each of the stages 14 to 16, the first stage 14 being the resistance path to the temperature sensor 21, and the second stage 15 being the compensation resistance 22.
To the resistance path 20 to the measuring resistance 23
The resistance path 20 for the heating resistance 24 and on the other hand the resistance path 20 for the heating resistance 24. Here, the resistance path 23 is arranged on the same side of the substrate 11, here on the upper side, and the temperature sensor 3
The same applies to 1 and the compensation resistor 22. On the other hand, the heating resistor 24 is arranged on the opposite side of the substrate 11, the lower side of the substrate, and the third stage. Width of steps 14-16, ie resistance path 2
The width of 0 decreases from the leading inflow side edge 12 of the substrate 11 to the outflow side edge 13. Two slits 25 and 26 are arranged perpendicularly to the flow direction together with the inflow side edges 17 and 18, and these slits are used for temperature decoupling between the resistance paths 20.

Five contact connecting surfaces 31 to 35 are arranged and applied along the longitudinal side opposite to the stepped longitudinal side of the measuring element 10. These connecting surfaces are arranged on the upper side of the substrate 11 at intervals. This upper side also supports the resistance path 20 for the temperature sensor 21, the compensation resistance 22 and the measuring resistance 23. The contact connection surfaces 31 to 35 are connected to the individual resistance paths 20 via printed conductor paths 19. That is, the contact connection surface 31 has the temperature sensor 21.
And the contact connection surface 32 has a compensating resistor 22 and a measuring resistor 23.
And the two contact connection surfaces 34, 35 are connected to the heating resistor 24. Furthermore, the conductor track 19 connects the temperature sensor 21 with the compensation resistor 22. The compensation resistor 22 can be tapped out by the contact connection surface 36. Measuring element 10
To the contact connection surfaces 31 to 35 of the above, the components of the circuit of the normal hot film type air mass meter according to the circuit diagram shown in FIG. 1 are connected. At that time, the temperature sensor and the compensating resistor 2 on the one hand
2, on the other hand, the series circuit with the measuring resistor 23 has two resistors 2
Together with 7, 28 form a Wheatstone bridge circuit, the bridge diagonal voltage of which is applied to a control amplifier 29 configured as a differential amplifier. A DC voltage source 30 is used to supply current to the Wheatstone bridge circuit.
The output voltage UA of the control amplifier 29 is applied to the heating resistor 24.

The operation of a hot film air mass meter known per se is briefly described below.

The heating current is heated by the output current of the control amplifier 29. The heating capacity of the heating resistor 24 is substantially determined by the bridge diagonal voltage of the control amplifier 29. This causes the heating resistor 24, which is in good thermal contact with the measuring resistor 23, to be brought to a high temperature which is much higher than the temperature of the flowing air. When the amount of air flowing through the measuring element 10 changes, the temperature of the measuring resistor 23 changes due to the change of convective heat transfer, and the Wheatstone bridge circuit detunes. Based on this, the control amplifier 29 changes the output current to the heating resistor 24. The change in the measuring resistance 23 due to the amount of heat flowing in and out through the closed control loop is
It is compensated by the heating capacity of the heating resistor 24. As a result, the measuring resistor 23 is always kept at a predetermined temperature. In this way, the heating current or output voltage U of the control amplifier 29 is
A is a measure for the flow of air. The temperature fluctuation of the flowing air is corrected by the series circuit of the temperature sensor 21 and the compensation resistor 22.

The temperature sensor 21 or the compensation resistor 22 or the resistance path 20 of each of the measuring and heating resistors 23, 24.
Has one unique inflow side edge or 17 to 18, so that the measuring element 10 has individual steps on the substrate 1
Spreading vertically above and below 1 is not sensitive. The widened portion may occur after the slits 25 and 26 are provided. This is because, even if the individual stages 14 to 16 are widened, the inflow-side part of the individual resistance path 20 remains largely unaffected by the preceding stages 14 to 15. To adapt to the surrounding flow,
The inflow edges 17, 18, 19 can be modified as required.

The measuring element 10 'of FIG. 2 corresponds to the measuring element 1 of FIG.
0, the outer contour, and the distribution arrangement of the resistance paths 20 on the surface of the substrate 11 are different. The outer contour is rectangular here. Figure 1
The same components as those in FIG.
The resistance path 20 for the temperature sensor 21 is again the substrate 11
The resistance path 20 for the measuring resistor 23 and the heating resistor 24 is arranged in the vicinity of the inflow side edge 12 of the substrate 1. The resistance path 20 for the compensation resistance 22 is behind the resistance path 20 of the temperature sensor 21 when viewed in the flow direction. The two resistance paths 20, the measuring resistance 23 and the heating resistance 24, are arranged laterally offset with respect to two other resistance paths 20 (which are also applied to the upper side or the lower side of the substrate 11). ing. Therefore, the surface region 38 of the substrate 11 in front of the measuring resistor 23 in the flow direction 37 is not covered. Furthermore, the "hot area" of the measuring element 10 ', which is formed by the heating resistance 24 and the resistance path 20 of the measuring resistance 23, is separated by the slit 39 from the other two resistance paths 20 for the temperature sensor 21 and the compensating resistance 22. There is. The slit 39 is parallel to the flow direction, starting from the outflow side edge 13 and starting from the substrate 1
It is installed in one. This forms a temperature decoupling for the temperature sensor and the compensation resistor. The inflow side edge 12 of the measuring element 10 'is shaped here in a wedge-shaped manner in order to favor the flow. The individual resistance paths 20 are again connected to the contact connection surfaces 31 to 35 via the conductor paths 19. The circuit arrangement shown therein is connected to the contact connection surface in the same way as in FIG.

This embodiment of the measuring element 10 'also has the advantage of being insensitive to the extent of the substrate area separated by the slit 39. The course of the slits is arranged parallel to the air flow direction 37, so that the inflow side of the individual resistance path 20 remains unaffected during expansion. The characteristic curve of the temperature element 10 'does not change because the inflow side does not change even when it spreads. The measuring element 10 ′ has the advantage over the measuring element 10 that the outer contour is simple. This simple outer contour can be well created from a large substrate. The configuration of FIG. 2 is also more robust against vibration and shock than the measuring element of FIG. This is because the vibration length is short and the measurement resistance and the heating resistances 23 and 24 can be formed in a rectangular shape.

[0019]

The invention avoids the drawbacks associated with finger spreading.

[Brief description of drawings]

FIG. 1 is a perspective view of an embodiment of the present invention.

FIG. 2 is a perspective view of another embodiment of the present invention.

[Explanation of symbols]

 10 Measuring Element 11 Substrate 12, 17, 18 Inflow Side Edge 13 Outflow Side Edge 14, 15, 16 Stage 20 Resistance Path 21 Temperature Sensor 22 Compensation Resistance 23 Measuring Resistance 24 Heating Resistance 29 Control Amplifier 30 DC Voltage Source 31-35 Contact Connection Surface 37 Flow direction 38 Surface area 39 Slit

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Claims (9)

[Claims] 1. A measuring element for a mass flow rate measuring device of a fluid medium, for example, intake air of an internal combustion engine, comprising a plurality of resistance paths exposed to the fluid medium, and a substrate supporting the resistance paths. In the measuring element in which the resistance paths are distributed on the substrate as follows, that is, the resistance paths for the measuring resistance are distributed in the flow direction in the vicinity of the outflow side edge behind the substrate. The surface area (38) of the substrate (11) has a flow direction (37)
The substrate area which is not covered between the front inflow edge (12) and the resistance path (20) for the measuring resistance (23) and which supports the resistance path (20) for the measuring resistance (23) is Measuring element characterized in that it is separated from each other resistance path (20) by a slit (39) extending in the direction (37) and originating from the outflow side edge (13) of the substrate (11). 2. A measuring resistor (23) and a heating resistor (2)
The resistance path (20) for 4) is arranged above and below the substrate (11), the resistance path (20) for the measuring resistance (23) being provided.
2. The measuring element according to claim 1, wherein is arranged with the other resistance path (20) on the upper side of the substrate (11). 3. A temperature sensor (21) and a compensation resistor (2
The resistance path (20) for 2) is arranged in succession with respect to each other in the flow direction, the resistance path (20) for the measuring resistance (23) and the heating resistance (24) being the resistance path (22) for the compensating resistance (22). Two
3. The measuring element according to claim 2, which is laterally offset from the slit (39) with respect to 0). 4. A measuring element for a mass flow rate measuring device of a fluid medium, for example, intake air of an internal combustion engine, comprising a plurality of resistance paths exposed to the fluid medium, and a substrate supporting the resistance paths. In the measuring element in which the resistance paths are distributed on the substrate as follows, that is, the resistance paths for the measuring resistance are distributed in the flow direction in the vicinity of the outflow side edge behind the substrate. The resistance paths (20) are arranged in a stepwise manner in succession with each other in the flow direction (37), with steps (15, 16) projecting from the preceding resistance path (20), respectively. 11) corresponds to the step shape of the resistance path (20) so that one inflow side edge (12, 17, 18) is formed along each step (14-16) of the resistance path (20). A measuring element characterized by being configured. 5. A slit (2) for temperature decoupling of the resistance path (20) is provided at the extension of the inflow side edge (17, 18).
5, 26), the slits extending parallel to one another and perpendicular to the flow direction (37). 6. A resistance path (2) arranged in series with each other.
The width of 0) seen in the flow direction decreases from the front inflow edge (12) in the flow direction (37) to the rear outflow edge (13) of the substrate (11) and the compensation resistance (22 The resistance path (20) for the temperature sensor (21) and the measurement resistance (23)
The resistance path (20) to the
The measuring element according to claim 4 or 5, which is arranged on the same upper side of (11). 7. A resistance path (2) for the heating resistance (24).
7. The measuring element according to claim 6, wherein 0) is arranged on the lower side of the substrate, and the resistance path (20) for the measuring resistance (23) is arranged directly opposite. 8. The resistance path (20) is electrically connected to the contact connection surfaces (31 to 35) arranged on the upper side of the substrate (11), and the contact connection surfaces are used for connecting devices. Item 7. The measuring element according to any one of Items 1 to 7. 9. Inflow edge (12; 1) of the substrate (11).
2. The measuring element according to claim 1, wherein 2, 17, 18) are adapted to flow and are configured, for example, in a wedge shape.